1. Field of the Invention
The present invention relates to electrode connection methods, electrode surface activation apparatuses, electrode connection apparatuses, connection methods of electronic components, and more particularly to an electrode connection method, an electrode surface activation apparatus and an electrode connection apparatus that connect electrodes by solid state bonding, a method of directly connecting components to be connected via the respective electrodes, and a connected structure including electrical components connected by the method.
2. Description of the Related Art
The demand for high density mounting of electronic components is increasing based on smaller and thinner electronic equipment of these years. Thus, when connecting an electronic component such as a semiconductor chip to a board, a mounting method of flip chip bonding a bare chip provided with protruding electrodes (bumps) to a board is often employed. Protruding electrodes are formed on a semiconductor chip used for flip chip bonding, and it is necessary to electrically connect the protruding electrodes to the wiring on the board.
The major example of protruding electrodes of an electronic component is solder bumps. There is the reflow soldering method as a method of connecting the electronic component to the circuit board in a case where the solder bumps are used. In the reflow soldering method, flux for eliminating an oxide film on the solder is applied to the electrodes on a board so as to improve the solder bonding. Then, the electronic component is positioned and mounted on the board. Thereafter, the electronic component and the board are electrically connected by the reflow such that the solder bumps are melted in a furnace having an air atmosphere or a nitrogen atmosphere so as to wet the electrodes of the board with the melted solder and spread the solder on the electrodes. Generally, the electronic component and the circuit board are mechanically connected by filling and curing a resin for sealing between the electronic component and the circuit board. The reflow soldering method is also employed when forming a stacked structure by stacking electronic components.
Recently, solid state bonding has been attracting attention as a method of mounting a highly integrated smaller semiconductor device to a board at low temperature and low pressure with high reliability and low damage. As a specific connection method of solid state bonding, a method is known where bonding surfaces of electrodes (for example, the electrodes of a semiconductor device and the electrodes of a board to which electrodes the electrodes of the semiconductor are connected) are placed in direct contact with each other and pressed so as to form a solid state bond. More specifically, a method is known where a firm bond (solid state bond) is formed between metal atoms at room temperature, after activating the surface of the metal forming the electrodes by eliminating an oxide film existing on the surfaces of the electrodes.
However, when a pollutant or an oxide film such as an oxide exists on the bonding surfaces, it is impossible to form a firm solid state bond of metal atoms. Accordingly, when forming the solid state bond, the elimination of the oxide film and activation are performed on the bonding surfaces.
As specific methods of eliminating the oxide film of the bonding surfaces so as to activate the bonding surfaces, there are a method of irradiating an inert gas ion beam or an inert gas high-speed atom beam on the bonding surfaces, a method of applying ultrasonic waves to the bonding surfaces, a method of applying friction to the bonding surfaces, and so on.
In addition, after activating the electrodes by the above-described methods, until the electrodes are connected to each other, it is necessary to maintain the state where the surfaces of the electrodes are activated. This is because even if the elimination of the oxide film of the bonding surfaces and the activation process of the bonding surfaces are performed, when the bonding surfaces are returned (exposed) to the air, the oxide film is formed on the bonding surfaces again.
Therefore, conventionally, when the elimination of the oxide film and the activation process end, the activated electrodes are maintained in a vacuum or an inert gas atmosphere. Further, the connecting process of the electrodes is performed in the same atmosphere.
However, when the above-described conventional methods are employed, until the solid state bond is formed after the activation of the electrode surfaces, it is necessary to maintain the state where the electrodes are activated. For this reason, a mechanism is required for maintaining the electrode surfaces in the vacuum or the inert gas atmosphere.
Accordingly, it is impossible to use a flip chip bonder capable of connecting the components in the air and having a high mounting speed. Thus, there has been a problem in that the efficiency of the connecting process of the electrodes is degraded. In addition, in order to make the connecting process more efficient, when the mechanism for realizing the inactive gas atmosphere is provided to the flip chip bonder, the equipment becomes complex and expensive. Thus, the equipment cost increases.
In addition, in the above-described reflow soldering by the solder bumps, since the melting point of the solder is generally high such as equal to or more than 200xc2x0 C., there is a possibility of the electronic component being thermally damaged. Moreover, shorts tend to occur between the adjacent electrodes when the solder melted in the reflow flows out from the electrode areas. Further, since the thermal expansion coefficient of the electronic component and the thermal expansion coefficient of the circuit board are different, shearing stress and strain are applied to the bonded parts connected by the reflow solder. Accordingly, the reliability of the connection is likely to be reduced.
On the other hand, in the method of forming the solid state bond such that the bonding surfaces are in direct contact with and pressed against each other after cleaning and activating the electrode surfaces of the components to be connected, it is difficult to achieve firm connection. The reason is that, since irregularities on the order of submicrons or microns originally exist on the electrode surfaces, the planarization of the electrode surfaces is difficult to achieve even if the electrode surfaces are cleaned, and thus the effective contact area of the electrodes is small. When the force on the connection is increased so as to improve the connection strength, the electronic component may be damaged. Additionally, when a polarization process such as the chemical-mechanical polishing (CMP) is performed so as to eliminate the irregularities on the electrode surfaces, problems such as an increase in the manufacturing cost and an increase in the TAT (turn around time) arise.
It is a general object of the present invention to provide an improved and useful electrode connection method, electrode surface activation apparatus, electrode connection apparatus, and connection method of electronic components in which the above-mentioned problems are eliminated.
It is another and more specific object of the present invention to provide an electrode connecting method, electrode surface activation apparatus, and electrode connecting apparatus that can simply and inexpensively form a solid state bond between electrodes.
It is still another object of the present invention to provide a method enabling the connection between an electronic component and a mounting board such as a circuit board or between electronic components with high reliability at low temperature and low load in which the above-described problems in the prior art are eliminated.
In order to achieve the above-mentioned objects, according to one aspect of the present invention, there is provided an electrode connecting method of connecting a first electrode and a second electrode, including the steps of: (a) activating respective bonding surfaces of the first and second electrodes; (b) coating each of the first and second electrodes having the activated surfaces with a coating member for maintaining the activated state; and (c) forming a solid state bond between the first and second electrodes by pressure welding the first and second electrodes so that the first and second electrodes break through the coating members.
According to the above-mentioned aspect of the present invention, the bonding surfaces are sealed (coated) with the coating member after performing the activation process on the bonding surfaces of the first and second electrodes. Thus, it is possible to maintain the state where the bonding surfaces are activated even when the first and second electrodes are placed (exposed) in the air.
In addition, when forming the solid state bond between the respective bonding surfaces of the first and second electrodes, each of the electrodes breaks through the coating member so as to form the solid state bond. Therefore, it is possible to form the solid state bond in the air. Hence, it is possible to correspond to the mass production process since the connecting in the air according to the flip chip method can be applied.
Additionally, according to another aspect of the present invention, in the above-described electrode connecting method, the activation may be performed by eliminating the oxide formed on the bonding surfaces, when activating the respective bonding surfaces of the first and second electrodes.
According to the above-mentioned aspect of the present invention, it is possible to connect the electrodes while maintaining the state where the surfaces of the electrodes of electronic components are activated by eliminating the oxide formed on the surfaces of the electrodes. For this reason, it is possible to achieve the improvement in the yield of the connecting process since the solid state bond having high reliability can be achieved with low temperature and low load.
In addition, according to another aspect of the present invention, in the above-described electrode connecting method, etching by irradiating plasma may be used as the activation process of activating the respective bonding surfaces of the first and second electrodes.
According to the above-mentioned aspect of the present invention, the bonding surfaces are activated by the plasma etching. Thus, it is possible to positively activate a plurality of electrodes at a high throughput.
Further, according to another aspect of the present invention, in the electrode connecting method, the reduction of a formic acid may be used as the activation process of activating the respective bonding surfaces of the first and second electrodes.
According to the above-mentioned aspect of the present invention, the bonding surfaces are activated by using the reduction of the formic acid. Hence, it is possible to surely activate the plurality of electrodes with inexpensive equipment.
Additionally, according to another aspect of the present invention, in the electrode connecting method, an adhesive film having an electrical insulation property may be used as the coating member for maintaining the activated state.
According to the above-mentioned aspect of the present invention, it is possible to easily perform the coating process for maintaining the activated state of the electrodes by using, as the coating member, an adhesive film having an electrical insulation property. In addition, it is possible to correspond to the automation of the coating process of the electrodes with ease.
Furthermore, according to another aspect of the present invention, in the electrode connecting method, the coating process of coating the first and second electrodes with the coating member may be performed in an inert gas atmosphere.
According to the above-mentioned aspect of the present invention, it is possible to maintain the activated state of the electrodes more positively, since the air causing the oxidization of the electrodes does not exist in between each of the electrodes and the coating member.
Additionally, according to another aspect of the present invention, in the electrode connecting method, the first and second electrodes may be protruding electrodes formed on the respective boards.
According to the above-mentioned aspect of the present invention, since the first and second electrodes are the protruding electrodes, when forming the solid state bond between the first and second electrodes by breaking through the coating member by the first and second electrodes, it is possible to positively perform the process of breaking through the coating member. Thus, it is possible to prevent the coating member from remaining in between the electrodes.
In addition, according to another aspect of the present invention, there is provided an electrode surface activation apparatus activating surfaces of electrodes, including: a first apparatus activating bonding surfaces of the electrodes; and a second apparatus coating the electrodes of which bonding surfaces are activated with a coating member for maintaining an activated state.
According to the above-mentioned aspect of the present invention, the bonding surfaces of the electrodes are activated by the first apparatus, and the activated electrodes are coated with the coating member by the second apparatus. Hence, it is possible to perform the process of applying the coating member to the electrodes with a simple construction.
In addition, according to another aspect of the present invention, in the above-described electrode surface activation apparatus, the first apparatus may activate the bonding surfaces of the electrodes by eliminating the oxide film formed on the bonding surfaces.
Further, according to another aspect of the present invention, in the above-described electrode surface activation apparatus, the first apparatus may etch the bonding surfaces by irradiating plasma so as to activate the bonding surfaces.
Additionally, according to another aspect of the present invention, in the electrode surface activation apparatus, the first apparatus may activate the bonding surfaces by using the reduction of formic acid.
Furthermore, according to another aspect of the present invention, in the electrode surface activation apparatus, an adhesive film having an electrical insulation property may be used as the coating member for maintaining the activated state.
In addition, according to another aspect of the present invention, in the electrode surface activation apparatus, the second apparatus may perform the process of coating the electrode with the coating member in an inert gas atmosphere.
Further, according to another aspect of the present invention, there is provided an electrode connecting apparatus, including an electrode surface activation apparatus and a bonding apparatus, the electrode surface activation apparatus including: a first apparatus activating bonding surfaces of the electrodes by eliminating an oxide on the bonding surfaces; and a second apparatus coating the electrodes with a coating member for maintaining an activated state, the electrodes having activated bonding surfaces, the bonding apparatus forming a solid state bond between a pair of electrodes by pressure welding the pair of electrodes so that the electrodes break through the coating member, the pair of electrodes having bonding surfaces activated by the electrode surface activation apparatus.
As mentioned above, according to the present invention, the bonding surfaces of the electrodes are activated by the electrode surface activation apparatus, the activated state of the electrodes are maintained by the coating member, and the electrodes are connected by the bonding apparatus. Accordingly, it is possible to form the solid state bond having high reliability in the bonding with low temperature and low load. At the same time, it is possible to correspond to the mass production processes, and thus the production cost can be reduced drastically.
Furthermore, according to another aspect of the present invention, there is provided a method of directly connecting components via respective electrodes, each components having an electrode and at least one of the components being an electronic component, including the steps of: (a) applying a metal material having a Young""s modulus equal to or less than 50 GPa to a surface of the electrode of at least one of the components; (b) activating a surface of the metal material and a surface of the electrode of the other component when the metal material is not applied to the surface of the electrode thereof; and (c) connecting the components by forming a solid state bond between the respective electrodes of the components via the applied metal material.
According to the above-mentioned aspect of the present invention, the respective electrodes of the components are connected while maintaining a state where the oxide on the electrode surface of the component and the oxide on the surface of the metal material for bonding are eliminated and activated. Thus, it is possible to form a solid state bond having high reliability in the connection between the components at low temperature and low load. At the same time, in the solid state bonding, the metal material for bonding does not flow out of the electrode areas, or the amount is very small even if the metal material flows out. Therefore, it is possible to effectively prevent the occurrence of a short between the adjacent electrodes, compared with the connection by reflow. Hence, it is possible to improve the yield of minute/narrow pitch connections of the semiconductor devices. In addition, labor-hours can be reduced since a leveling process such as CMP before connecting is not required.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the following drawings.